Differential impacts of nitrogen compounds on soil acid phosphatase activity in a meadow steppe

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BackgroundNitrogen (N) addition profoundly alters soil phosphatase activities and induces widespread microbial phosphorus (P) limitation in grassland ecosystems. However, the long-term effects of different rates and chemical forms of N addition on soil acid phosphatase (ACP) activity and P availability remain unclear. Here, based on a 10-year N addition experiment, we investigated the effects of a range of N addition rates (0–50 g N m−2 yr−1) applied as either (NH4)2SO4 or urea on ACP activity in a northern China meadow steppe, with and without mowing management.ResultsWe found that ACP activity remained unaffected by N addition until certain thresholds were reached (< 10 g N m−2 yr−1 for [(NH4)2SO4] and < 20 g N m−2 yr−1 for urea), beyond which it declined sharply. (NH4)2SO4 exerted a stronger inhibitory effect on ACP activity compared to urea, with the former primarily acting through soil acidification and the latter through a decrease in bacterial diversity. In contrast, mowing regimes did not significantly alter ACP activity under either N form.ConclusionsOur findings underscore the necessity of accounting for both N addition rates and N forms when assessing atmospheric N deposition impacts on soil phosphatase activity. These results inform the development of management strategies to mitigate declines in soil enzyme activity and enhance the long-term sustainability of grassland ecosystems.